1. Field of the Invention
This invention relates to a gas injection moulding needle and in particular to a valve arrangement for such a needle.
2. Background of the Invention
Gas injection moulding is a well established process. Needles are employed to inject and to vent gas used during the moulding cycle. The majority of needles operate with valve systems that rely on moving members; if high flow is to be achieved. Such valves allow rapid ingress and exhaust of gas to the mould. However such needles suffer the disadvantage that polymer may block the open end of needles and also feed back down the needle. This can also lead to blockage and/or accelerated wear of needle assemblies; in particular wear of spring and piston members.